DIY Stompboxes => Building your own stompbox => Topic started by: Bill_F on December 09, 2003, 06:09:01 AM

Title: Speakers for practice amp
Post by: Bill_F on December 09, 2003, 06:09:01 AM
I want to build one of the 386 practice amps. Anybody know a good place to get speakers here in the UK? I'm thinking of using a 4" (or a little over 100mm, still trying to get used to the metric system). Do you need something voiced for a guitar, or is any speaker OK?

Title: Speakers for practice amp
Post by: Ansil on December 09, 2003, 06:37:29 AM
i wuldnt use less than 8"
Title: Speakers for practice amp
Post by: Hungeryhippie on December 09, 2003, 07:17:32 AM
I used an elliptical speaker from one of those portable tape players/recorders. it was rated at 4 ohms and 2watts. It works great in a sealed enclosure, great for practicing at home. I think it is about 11cm at its longest and about 6cm widest width. Its more than loud enough (the woman downstairs to me will vouch for that!) I cant stop playing through it, and since I made it I use it for testing all my new pedals, cos its small enough to fit on the table with everything else!!  And most of all it was free!!!

Hope this helps
Title: Speakers for practice amp
Post by: Bill_F on December 09, 2003, 07:23:40 AM
Quote from: Ansil
i wuldnt use less than 8"

I have a nice little wooden box that somebody gave me that I want to  use. I think a 4" speaker is about all I can get into it. I'm trying to get something small that can sit on my desktop, like a Smokey but hopefully a bit better.
Title: Speakers for practice amp
Post by: Ansil on December 09, 2003, 07:30:36 AM
if you go with a small speaker.. try putting some glue on the cone to get it stiffer so maybe you will have some bass response.   you can put any speaker in there really  if you use one that has a piezo in it it won't sound too good..
Title: Speakers for practice amp
Post by: Ge_Whiz on December 09, 2003, 01:28:02 PM
Four inches is an unusual size for a speaker - they usually jump from three inches to 5.25".

Look around for a scrap car radio speaker with a hefty magnet - they are usually pretty good and can be picked up for a couple of quid. Ask in car shops that sell radios - not specialist hi-fi joints, but Halfords. Ask if they have a speaker from a pair where one has been damaged, but don't pay through the nose - £5 tops. Municipal waste sites often put old ghetto blasters to one side and sell 'em for £1 - rip the speakers out. Look in skips. Even a 3" in a sealed box will sound reasonable.

For a 386 amp, you don't need much power handling - Bardwell's list what seems to be a 4" square speaker, also a 75 x 50 elliptical. Try both. And stock up with resistors, capacitors and transistors at impossibly low prices while you are there! (Buy their BC549 transistor pack - 30 for £1.)

Also trying e-mailing J&N Factors (Bolney, Sussex) - and tell them what you're looking for. Some of their stuff is prehistoric, but by golly it's cheap. If they offer a choice, buy several!
Title: Speakers for practice amp
Post by: Mark Hammer on December 10, 2003, 11:00:49 AM
Once you go below 8", it is rare that there is any commercial speaker "voiced" for guitar.  On the other hand, all that voicing does is remove the obligation to EQ the signal in certain ways so that what comes out of the speaker is pleasing.  

The feedback loop between pin 8 and 1 on the 386 can be used to adjust the treble content, and the loop between the output at pin 5 and pin 1 can be used to adjust the bass content.  Read the datasheet and appnotes for the 386 and it will explain more or less how to do this.

Although a larger speaker will undoubtedly move more air and yield more bass, there are two things to consider: the role of the cabinet, and the role that a bigger and heavier cone will play in attenuating treble and bite.  Smaller speakers can sound decent but stick them in a cramped enclosure and they sound like you're playing into a soup can.  As for the role of cone size, I would certainly not expect a 1/2-W amp driven by a 9v battery going into an 8" speaker to reveal the inherent "quack" in a Strat or the twang of a good Tele bridge pickup.  Just not enough current drive to make the speaker play those treble peaks.  Of course if all you want it for is tuning up that's another thing.

At the very least, you want something described as a "full-range" speaker.  Just about everything less than 4" most assuredly is, though a number of 4"-8" speakers are not.  So check.  I've had pretty good luck with a variety of 6" and 8" full-range speakers that are typically used for those ceiling intercoms.  They are intended to handle a modest signal (usually <15w) and are efficient and responsive enough that a half-watt will move them adequately.
Title: Speakers for practice amp
Post by: jsleep on December 10, 2003, 04:23:29 PM
I bought a 6" JENSEN MOD SERIES, 15 W, 4 OHM speaker for this purpose, but I haven't had a chance to try it out yet!  I would think this would be a good option, since it _is_ a guitar speaker.  They are inexpensive and have a huge magnet compared to the other small speakers available.  Maybe this is too big for your purposes.

Title: Speakers for practice amp
Post by: javacody on December 10, 2003, 08:03:39 PM
I got an 8" Jensen vintage series (Ceramic) for $20! It is a little larger, but still small enough for a portable amp. It sounds very good.
Title: Speakers for practice amp
Post by: brett on December 11, 2003, 12:33:47 AM
In my test rig I use a fair of 5 inch car speakers (Pioneer brand, I think) - they're surprisingly good for about 10 of your pounds (on sale).  So I think there ARE going to be SOME 4 inch speakers with reasonable bass performance.  And you can always turn the bass up a bit more. :D
Title: Practice Amp speakers
Post by: Guido Landry on December 11, 2003, 04:21:52 AM
While developing my 1W (Schematics 2) valve amp, I tried various speakers they had to be small for a small amp sound and to be compact.
Guitar speakers are opposite to HiFi speakers. They require stiff cone support at the edges and a soft paper cone - this is how you get treble out of a 12" speaker - The larger the magnet the higher the efficiency.
 I tried a cheap elliptical TV speaker, but it was too harsh and broke up - resonated - with low frequency signals.
My Celestion G12 M70 sounded great and was loud - but too expensive and bulky but is used as an external cabinet on occasions
A cheap 8" PA speaker costs about 3 pounds and can be found at RS components had enough bass responce but was too shrill until I performed a bit of surgery by removing the small inner cone with a razor blade. The speaker now sounds pretty good and gives ample volume while overdriving the amp without disturbing the family while they watching TV.
Title: Speakers for practice amp
Post by: Jered on December 11, 2003, 07:22:39 AM
JD, did you buy the 6" Jensen online? I'm looking for a good 6" speaker.
      Thanks,  Jered
Title: Speakers for practice amp
Post by: Nasse on December 11, 2003, 01:07:06 PM
I dont have much experience using other than instrument speakers, though I killed with Marshall an old killer sounding 10" alnico speaker that I took from old tube radio.

I have Roland DAC-15 with 8" open back, and bass is not heavy. It was made with four small speakers version too. I bought at flea market an used small Ibanez bass amp and the speaker is smaller, maybe 6". I think they made it closed-back to give more bass. It gives some more lows than my Roland but it does not sound any better :wink:

Last summer I saw a self-made battery powered combo, some guys played in the street, mostly acoustic. It had six oval-shaped car speakers, and they played bass and some gtr through it. Maybe some car speakers that are designed to work without closed box have something similar with instrument speakers.